1. Field of the Invention
The present general inventive concept relates to threshold voltage control, and more particularly, to methods and apparatuses to adjust threshold voltages of a transmission envelope detector during serial communication.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional serial communication system. Referring to FIG. 1, the serial communication system 10 includes a first device and a second device, which are connected to each other through a communication channel 30 for serial communication. The first device includes an analog front end (AFE) 20 and a controller 25. The second device includes an AFE 40 and a controller 45.
For example, the first device can be a host like a computer and the second device can be a data storage device such as a hard disc drive.
Each transmitter 21 and 41 of the respective AFE 20 and 40 receives each transmission signal Tx_DATA and Tx_DATA′ to transmit and transmits each differential signal Txp and Txn, Txp′ and Txn′ to each receiver 27 and 47 of the respective AFE 20 and 40 through a communication channel 30.
Each transmission envelope detector 23 and 43 detects (or discriminates) whether the communication channel 30 is in an unsquelch state or a squelch state based on a voltage gap (or, difference) of each differential signals Rxp and Rxn, Rxp′ and Rxn′ received through a communication channel 30 and a voltage gap of threshold voltages predetermined in advance. And then, each transmission envelope detector 23 and 43 outputs each indication signal according to a result of detection to each controller 25 and 45.
When the state of the communication channel 30 is in the unsquelch state, the first device and the second device may perform serial communication to each other. However, if the state of the communication channel 30 is in the squelch state, the first device and the second device may not perform serial communication to each other.
Each transmission envelope detector 23 and 43, which is also named as a squelch detector, detects voltage levels of the differential signals Rxp and Rxn, Rxp′ and Rxn′ input through a communication channel 30 based on threshold voltages, for example, squelch threshold voltages predetermined in advance, discriminates if a signal or data of the communication channel is a valid signal (or valid data) or noise based on a result of detection, and outputs a result of discrimination.
Each controller 25 and 45 may output enable signals EN and EN′ making each receiver 27 and 47 enabled or may output disable signals DIS and DIS′ making each receiver 27 and 47 disabled in response to each of the indication signals.
FIG. 2 illustrates waveforms of signals when an initialization of communication is successful. FIG. 3 illustrates waveforms of signals when an initialization of communication fails.
Referring to FIGS. 1 and 2, when a difference VdiffRX between differential signals Rxp and Rxn, which are initially input to a transmission envelope detector 23 through the communication channel 30 performing serial communication, is greater than a difference SQ_TH1 between threshold voltages of the transmission envelope detector 23 set in advance (i.e., an initialization of communication is successful) resulting in a signal or data of the communication channel 30 being considered a valid signal or valid data (i.e., a state of the communication channel 30 is unsquelch), the transmission envelope detector 23 outputs an indication signal having a high level.
The controller 25 outputs an enable signal EN to a receiver 27 in response to the indication signal. Because the receiver 27 is enabled in response to the enable signal EN, the receiver 27 receives and processes differential signals Rxp and Rxn input through the communication channel 30 and outputs the processed valid signal or valid data Rx_DATA to another block.
However, referring to FIGS. 1 and 3, when the difference VdiffRX between differential signals Rxp and Rxn, which are initially input to the transmission envelope detector 23 through the communication channel 30 performing the serial communication, is less than the difference SQ_TH1 between threshold voltages of a transmission envelope detector 23 set in advance (i.e., when an initialization of communication fails), resulting in a signal or data of the communication channel 30 being considered noise (i.e., a state of the communication channel 30 is squelch), the transmission envelope detector 23 outputs an indication signal having a low level. Here, threshold voltages of the transmission envelope detector 23, which are once set up, cannot be changed.
The controller 25 outputs a disable signal DIS to a receiver 27 in response to the indication signal. The receiver 27 is disabled in response to the disable signal DIS, so that the receiver 27 cannot receive differential signals Rxp and Rxn input through the communication channel 30.
As described above, the transmission envelope detector 23 may protect an AFE 20 from a noise input through the communication channel 30.
However, when a noise having a greater difference than the difference SQ_TH1 between threshold voltages of the transmission envelope detector 23 set in advance while the first device and the second device are communicating through the communication channel 30, the first device and the second device may be damaged as the noise can be input to a receiver 27 of the first device or a receiver 47 of the second device.
Therefore, by changing threshold voltages of the transmission envelope detector 23 set in advance after the first device and the second device start communication, methods and apparatuses to intercept the noise are required even when a noise is input, which has the greater difference than a difference between threshold voltages of the transmission envelope detector 23 set in advance, after the communication is started.